Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

634
FXUS63 KLOT 270747
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
247 AM CDT Mon Apr 27 2026

.KEY MESSAGES...

- There is a low (10 to 20%) chance of damaging non-
  thunderstorm wind gusts today north of I-80 between noon and 3
  PM.

- There is a threat for severe weather today, primarily between
  4 and 11 PM this evening. The main threats are damaging winds
  and damaging hail.

- A transition toward a cooler and drier pattern will commence
  by midweek.

&&

.DISCUSSION...
Issued at 247 AM CDT Mon Apr 27 2026

Early morning radar, satellite, and ASOS/AWOS observations
depict a developing surface low in far southwestern Kansas with
an associated broad warm frontal zone extending eastward through
central Missouri and into far western Tennessee. Broad
southwesterly flow continues to advect an EML plume across the
central Plains, which with a developing low-level jet (some
50-60kt per regional VWPs) and the approach an unbalanced
upper-level short-wavelengh trough propagating into the
Southern Plains, is supporting an expansive region of elevated
gravity wave associated convection (GWAC) across central Kansas
at press time.

Owing to continued synoptic-scale ascent facilitated by the
developing surface low and upper-level trough as well as a
steady northeasterly feed of instability through the night, the
expectation is for the ongoing elevated convection across
central Kansas to coalesce into a bore-driven mesoscale
convective system over the coming hours. The orientation of the
low-level jet and instability axis would then guide the
convective system through Kansas City, Missouri by daybreak and
into central Illinois (along/south of I-80) by mid to late
morning. With instability decreasing with eastward extent, the
convective system should begin to weaken as it crosses the I-39
corridor in central Illinois. With that said, northeasterly-
oriented deep-layer shear vectors will promote a broad
stratiform precipitation region j(perhaps with embedded
thunder) on the northern side of the zone of active convection
across northern Illinois/southern Wisconsin. The severe weather
threat with the first batch of activity is currently thought to
be low (call it a 5 to 15% chance at any given point) owing to
meager instability. With that said, locally damaging winds
cannot be ruled out particularly south of I-80 with any
decaying convective element.

Outside the convection this morning, do have growing concern
for a period of non-thunderstorm damaging winds mainly
along/north of I-80 between noon and 3 PM along the backside of
the decaying stratiform region this afternoon. CAM guidance has
remained remarkably consistent in depicting rapid
drying/subsidence along the backside of the stratiform region,
which would support the development of a very tight pressure
gradient behind the leading meso-high (a wake- low situation).
The HRRR has long had the signal for nearly 24 hours now,
including explicit wind gust output up to 75 mph in the most
recent iteration. It`s always tough to go all-in on these sorts
of features given inherent dependencies on how convection
evolves and a history of false alarms of such by CAM guidance.
With that said, will give a very hearty warning to the incoming
day shift to keep an eye out for even the slightest signs of
wake low development to get lead time on what would probably be
a short- fused High Wind Warning.

Attention then turns to the threat for severe weather this
afternoon and evening. There is excellent agreement among
deterministic and ensemble guidance that the upper-level
shortwave currently propagating into the Central Plains will
lift into the Great Lakes region this afternoon, allowing the
aforementioned surface low to track from roughly Kansas City, MO
this morning to near La Crosse, Wisconsin this evening. As the
upper-level wave passes overhead, an associated 75kt 500mb speed
max will arc directly across the Mississippi River as pressure
falls in the central Great Lakes induce the rapid
intensification of the 925- to 850mb wind field. The kinematic
environment will thus become very supportive of organized
convection by this evening.

Meanwhile, increasing isentropic ascent atop the (what will be
outflow-reinforced) warm front will set the stage for festering
convection from eastern Missouri into central Illinois during
the afternoon hours. Even with increasing synoptic southwesterly
flow, a steady feed of cool outflow from the festering
convection will likely impede the northeastward progression of
the warm front, and hence, instability, into area area by early
evening. Heavy cloud cover throughout the day will also hamper
the ability for low-level lapse rates to steepen and surface
temperatures to warm, with highs only poised to make it into the
upper 60s to perhaps locally 70. Nevertheless, cooling mid-
level temperatures (by virtue of synoptic-scale ascent and the
continued advection of an EML plume via southwesterly mid-level
flow) will nevertheless support the development of elevated
instability throughout the afternoon.

Even with a lack of surface-based instability, we still do
expect the rapid development and expansion of convection across
our area this afternoon as the arrival of the upper-level
shortwave interacts with the elevated instability axis.
Accordingly, we continue to see a threat for severe weather this
afternoon and evening in our local area mainly in the form of
locally damaging winds and hail. The inability for the surface-
based instability axis to make it into our area should relegate
the (what will be a higher-end) tornado threat south of our area
across central and southern Illinois, but tracking the exact
location of the warm front will be important in case it does
sneak into our area. So, today still looks active, just not
necessarily what initially looked like a very concerning
scenario in our local area. In collaboration with SPC, the Level
3/5 threat area has been adjusted southward to be closer to the
expected position of the outflow-reinforce warm front this
afternoon.

In spite of the most likely outcome outlined above, do still
feel the need to discuss the low-probability scenario in which
the surface-based instability does make it into our area.
Should convection across central Nebraska fail to coalesce into
a bore-driven MCS (as it has struggled to do so thus far and
instead remain as GWAC), or the convective footprint into
central Illinois is minimized by early afternoon (so no outflow
to counteract southwesterly flow), the safeguard of festering
convection limiting the northeastward-movement of the warm
front would fail to materialize. In such a scenario, the warm
front would be able to lift into at least northwestern Illinois,
leading to a narrow zone where surface-based instability would
overlap with an intense kinematic environment. Should this
occur, a band of supercells with a threat for all hazards
including tornadoes would materialize near the Mississippi River
with upscale growth into an intense squall line thereafter.
Would have to think that instability would still decrease with
eastward extent toward Lake Michigan... though there would still
a more pronounced threat for an all-hazard severe weather
event. Most guidance does not support this outcome at this point
in time, though it does remain completely realistic provided a
lot of dominoes fall in the wrong direction.


Tuesday onward:

The upper-level pattern will undergo a substantial pattern
shift through the rest of the week with predominant aggregate
troughing along the US/Canadian border. As a result, the
expectation is for cooler and drier conditions to prevail with
highs in the 60s and overnight lows in the upper 30s to lower
40s. We can easily envision a threat for frost by the weekend.
Thereafter, long-range ensembles advertise warming trend during
the first week of May.

Borchardt

&&

.AVIATION /06Z TAFS THROUGH 12Z TUESDAY/...
Issued at 1231 AM CDT Mon Apr 27 2026

Forecast concerns include...

Scattered thunderstorms late this afternoon thru mid evening.
Strong/gusty southeast winds today.
Chance of showers mid morning thru early afternoon.

East/southeast winds are expected to slowly increase early this
morning with gusts into the 20kt range possible. Speeds/gusts
will steadily increase after sunrise, in the mid 20kt range by
mid morning and then into the 30kt range this afternoon.
Directions will slowly become southeasterly later this morning
and then south/southeasterly this afternoon, likely turning
southerly late in the afternoon or early evening. There may be a
few hour period in the late afternoon when gusts into the mid
30kt range will be possible. Winds will turn southwest this
evening as gusts diminish some and then shift westerly early
Tuesday morning.

The current shower activity across eastern IA may reach RFD and
northwest IL in the predawn hours this morning. Additional
showers are expected to move across all of the terminals from
mid morning through early this afternoon. There may be some
thunder with this activity, especially south of the terminals
but low confidence at this time and maintained tempo shower
mention. A lull in the precipitation is expected during the
early/mid afternoon and then scattered thunderstorms are
expected to develop across northwest IL and quickly move east
across the terminals, possibly as a broken line of
thunderstorms.

Mvfr cigs, possibly ifr cigs can be expected with any of the
thunderstorms then prevailing mvfr cigs are expected to develop
across the entire area early Tuesday morning. cms

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory until 10 AM CDT Tuesday for the IL
     nearshore waters.

     Small Craft Advisory from 10 AM this morning to 10 AM CDT
     Tuesday for the IN nearshore waters.

&&

$$

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